Projection systems, for projecting an image on to a screen, use several different components for providing efficient illumination of an imager. Projection systems typically use a lamp to generate the illumination light, with several optical elements being interposed between the lamp and the imager display device to transfer the light to the image display device. The image display device imposes an image on a beam of light. It may perform this function through different mechanisms, for example by absorption, as with a photographic slide, by polarization, as with a liquid crystal display (LCD), or by diverting the light, as with a micromechanical array of individually addressable, tiltable mirrors.
Characteristics that are important in projection systems include the brightness and the contrast of the image. It is often the case that one characteristic may be improved, but at the expense of another characteristic. It is, therefore, important to be able to increase contrast while reducing the negative impact on image brightness and to increase image brightness while reducing the negative impact on contrast.